1. Field of the Invention
The present invention relates to a polyoxyalkylene polyol, a polymer polyol, and a process for preparing a polyoxyalkylene polyol, a polymer polyol or a flexible polyurethane foam. Particularly the invention relates to a polyoxyalkylene polyol having a hydroxyl value of 10 to 35 mg KOH/g, a monool content less than or equal to 15 mol % and a Head-to-Tail bond selectivity greater than or equal to 96 percent resulting from addition polymerization of propylene oxide, a process for preparing the same and a process for reacting an organic polyisocyanate with the above-mentioned polyoxyalkylene polyol in the presence of a catalyst, a surfactant, a foaming agent, a crosslinking agent and other additives to prepare a flexible polyurethane foam improved in humid aged compression set, and further relates to a polymer polyol comprising (a) a polyoxyalkylene polyol having a hydroxyl value of from 10 to 35 mg KOH/g, a monool content less than or equal to 15 mol % and a Head-to-Tail bond selectivity greater than or equal to 96 percent resulting from addition polymerization of propylene oxide, and (b-1) polymer particles which are dispersed in the polyoxyalkylene polyol in the range of from greater than or equal to 5 wt % to less than 30 wt % or (b-2) polymer particles which are dispersed in the polyoxyalkylene polyol in the range of from greater than or equal to 30 wt % to less than or equal to 60 wt % and have a glass transition temperature of from 90 to 120 .degree. C., and processes for preparing the same and a process for preparing a flexible polyurethane foam comprising reacting an organic polyisocyanate compound with a polyoxyalkylene polyol containing at least one of the above-mentioned polymer polyol in the presence of a foaming agent, a catalyst, a surfactant, a crosslinking agent and other additives.
2. Prior Art
Potassium hydroxide is mainly used as a catalyst in the preparation of polyoxyalkylene polyols for polyurethane raw materials and others. It is well-known that when propylene oxide as an alkylene oxide is added and polymerization is carried out, it causes side-reactions in which monool are formed, and when the molecular weight of polyoxyalkylene polyols is increased, the monool amount is increased. It is thought that when the polyol has a large amount of monools, cross-linking and polymerization are prevented in the urethane reaction of a polyoxyalkylene polyol with an organic polyisocyanate compound, and the thus-obtained flexible polyurethane foam and elastomer are deteriorated in mechanical properties.
In a conventional process such as the addition polymerization of propylene oxide to an active hydrogen compound by using a potassium hydroxide catalyst, the monool content of polymerized polyoxyalkylene polyol having a hydroxyl value less than or equal to 35 mg KOH/g exceeds 15 mol % and it is substantially impossible to prepare a polyoxyalkylene polyol having a hydroxyl value less than or equal to 28 mg KOH/g.
U.S. Pat. No. 3,829,505, JP-A-2-115211 (Tokkaihei) and JP-A-3-14812 (Tokkaihei) disclose processes for using catalysts other than alkali metal catalysts, such as a double metal cyanide complex catalyst in the addition polymerization of propylene oxide as an alkylene oxide to solve the above-mentioned problems. Particularly, JP-A-3-14812 (Tokkaihei) discloses in the comparative examples that double metal cyanide complex catalysts are superior to catalysts containing alkali metal hydroxide. However, there is a problem that these catalysts are extremely expensive and less economical on an industrial scale, and when the addition polymerization of ethylene oxide as an alkylene oxide is carried out, the process needs further removing catalyst and carrying out another polymerization with an alkali metal hydroxide or its alkoxide.
Polyoxyalkylene polyols containing less amounts of monools have a tendency to have a higher viscosity. When a double metal cyanide complex catalyst is used, they have a tendency to have a strikingly high viscosity. It seems to result from their lower Head-to-Tail bond selectivity in the addition polymerization of propylene oxide as an alkylene oxide. When they have a higher viscosity, troubles of molding stability and mixing properties occur in the mechanical molding of flexible polyurethane foams, and high molecular weight polyoxyalkylene polyols are limited for their use.
It is, however, expected that a polymer polyol which has as a matrix a polyoxyalkylene polyol having a large amount of monools as mentioned above also decreases the physical properties of a polyurethane foam and the like.
To solve the above-mentioned problems, U.S. Pat. No. 3,829,505, JP-A-02-115211 (Tokkaihei) and JP-A-03-014812 (Tokkaihei) disclose a process for preparing a polyoxyalkylene polyol in which a catalyst other than an alkali metal catalyst such as a double metal cyanide complex catalyst is used as a catalyst in the addition polymerization of propylene oxide as alkylene oxide and also disclose a polymer polyol wherein the above-mentioned polyoxyalkylene polyol is a matrix. There is a trend that a polyoxyalkylene polyol having a small amount of monools has higher viscosity. Preparation of a polyoxyalkylene polyol by using a double metal cyanide complex catalyst causes a remarkable viscosity increase of polyoxyalkylene polyol. The viscosity increase is due to the low Head-to-Tail bond selectivity in the addition polymerization of propylene oxide as an alkylene oxide. Therefore, it is expected that a polymer polyol resulting from the procedure of radical polymerization of an ethylenically unsaturated monomer in a polyoxyalkylene polyol has also remarkably high viscosity. When a polymer polyol has high viscosity, there are an obstacle to stable molding and mixing in the mechanical molding for manufacturing a flexible polyurethane foam and a limit on the use of a polymer polyol wherein a high molecular weight polyoxyalkylene polyol is a matrix.
Polymer polyols have inferior dispersion stability and higher viscosity. Especially when the polymer content is greater than or equal to 30 wt %, such tendencies are remarkable. It is substantially impossible to prepare a polymer polyol which has high polymer concentration in a polyoxyalkylene polyol as a matrix by using the above-mentioned metal complex catalyst.
It is also known to use a chain transfer agent to solve such problems as the inferior dispersion stability and higher viscosity of highly concentrated polymer polyol. U.S. Pat. No. 3,953,393 and JP-A-01-221403 (Tokkaihei) disclose processes for preparing polymer polyols of low viscosity by using alkylmercaptans as chain transfer agents. According to these processes, however, polymer polyols are bad-smelling and it is difficult to obtain an available polymer polyol because a highly concentrated polymer polyol cannot avoid a sudden viscosity increase.
JP-A-58-210917 (Tokkaisho) discloses a process for using, as a chain transfer agent, mercaptans, ketones, alcohols, aldehydes, halogenated compounds, benzene derivatives, and particularly isopropyl alcohol. The process is, however, insufficient to reduce the viscosity of highly concentrated polymer polyol. JP-A-63-146912 (Tokkaisho) discloses a process for using amines such as morpholines as reaction regulators and the process differs from that of the present invention because of using a special polyol.
Because flexible polyurethane foams have moderate elasticity and are more excellent in impact absorbing property, they are widely used for bedclothes, furniture, sheets of motor vehicles, cushions of furniture and so on. They are usually prepared through the slab or hot mold foaming method. They lack flexibility and have lower elasticity so that they lack the same pleasantness for people compared to rubber latex foam. High elasticity polyurethane foams have been developed to improve conventional flexible polyurethane foams in the above-mentioned properties. They are prepared through the process for reacting polyisocyanate with a polyoxyalkylene polyol and a polymer polyol used for part of the polyoxyalkylene polyol, the polymer polyol is obtained by polymerizing an ethylenically unsaturated monomer such as acrylonitrile, styrene and so on in a polyoxyalkylene polyol, and, after foaming, leaving the foam as it is at temperatures of from room temperature to 100.degree. C. for a short period. While sitting on the foams, people are impressed by their extremely excellent pleasantness so that the foams are widely used for cushions of cars and so on.
They are used for cushions of cars and have to be excellent in stiffness, i.e. hardness and mechanical properties, but are inferior in humid aged durability (hereinafter represented by the term humid aged compression set).
JP-A-63-75021 (Tokkaisho), JP-A-02-115211 (Tokkaihei), JP-A-03-068620 (Tokkaihei) and JP-A-03-014812 (Tokkaihei) disclose processes for improving polyurethane foams in humid aged compression set. JP-A-63-75021 (Tokkaisho) discloses that the use in combination of a special crosslinking agent serves to improve a polyurethane foam in humid aged compression set to some degree but excessive amounts of it deteriorate the foam in mechanical properties such as elongation, tear strength and so on, and there is a limit in the improvement of polyurethane foam in humid aged compression set. JP-A-02-115211 (Tokkaihei), JP-A-03-068620 (Tokkaihei) and JP-A-03-014812 (Tokkaihei) disclose that a polyoxyalkylene polyol having a less total unsaturation degree serves to improve a polyurethane foam in humid aged compression set. These polyoxyalkylene polyols are prepared in the presence of diethylzinc, metallic porphyrin or a double metal cyanide complex catalyst as disclosed in the above-mentioned specifications cited from opened patent official gazettes. According to the results double-checked by the present inventors, however, the flexible polyurethane foam resulting from a polyoxyalkylene polyol prepared by using the above-mentioned double metal cyanide complex catalyst and so on was not improved in humid aged compression set so much as the present inventors had expected.